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Seasonal and Diurnal Variability of Detached Dust Layers in the Tropical Martian Atmosphere Dr. Nicholas G. Heavens (Hampton University, nicholas.heavens@hamptonu.edu), Morgan S. Johnson (RIT, APS CURE Student), and the Mars Climate Sounder Science Teamnicholas.heavens@hamptonu.edu Two Instruments Looked at Mars, Day and Night. What They Found May Shock You. Figs. 1 and 2: Zonal average dust density- scaled opacity (m 2 kg -1 on a log 10 scale) for the times labeled, as observed by MRO’s Mars Climate Sounder [Heavens et al., 2011]. Fig 1c is model prescription of “Conrath- nu” profiles. Fig. 3: Zonal average dust mixing ratio (mb -1 ) as observed by MGS-TES for the dates labeled [Guzewich et al., 2013]. (What is plotted in Figs. 1, 2, and 3 are different are all proportional to the mass mixing ratio of dust.) THE TOP LINE (OBJECTIVES): The dust layer ~20 km above Mars’s tropics is thicker in the day than the night. Diurnal variability is stronger at northern summer solstice than at southern summer solstice. Q: Is this variability real or an artifact of averaging profiles from different parts of Mars in the day than during the night? Daytime, Northern Summer Solstice Nighttime, Northern Summer Solstice These Planetary Scientists from Hampton University Used One Weird Trick To Isolate Diurnal Change in Mars’s Temperature and Aerosol Structure Fig. 4: Selected MRO orbits over 2.5 days in late September of 2006 are plotted to show intersections between dayside and nightside orbits at approximately semidiurnal separation. We select retrievals from each dayside orbit that are within 140 km (a criterion derived from the spatial resolution of Mars Climate Sounder) of a retrieval on the succeeding nightside orbit and vice versa. Differencing these retrievals isolates dayside to nightside and nightside to dayside change. A zonal average of spatially coincident differences then can be made. Fig. 5: Mean change in labeled quantities for spatially contiguous profiles at semidiurnal temporal separation during a portion of MY 31 (L s =75°-145°). White marks where the average cannot be analyzed or has a magnitude less than 1.96  the standard error of the mean, which indicates that we cannot reject the null hypothesis that the mean is different than 0 (at 95% confidence). “PM-AM” refers to night to day change. “AM-PM” refers to day to night change. The temperature differences strongly resemble previously analyses of the diurnal tide. Hard Core Modelers Only: Once You See These, Your Friends Won’t Be Seeing Much of You And Now A Word From Our Sponsors Figs. 8 (top) and 9 (bottom): Cumulative distribution of night to day change (Fig. 8) or day to night (Fig. 9) in dust density-scaled opacity for the labeled seasons. Solid line is 0 contour, dashed red lines are +/- 10 -3 m 2 kg - 1. THE BOTTOM LINE (CONCLUSION): The size-frequency distribution of DDL formation and removal events in the tropics and in smaller regions can be characterized, providing an important test for future GCM parameterizations. This work was supported by NASA’s Jet Propulsion Laboratory, Caltech (subcontract 1471216). M.S. Johnson was hosted at Hampton University as part of the CREST Undergraduate Research Experience. Limb Obscuring Dust and Ice Hazes Hate Us For Revealing This Closely- Guarded Secret Fig. 6 (top left): Vertical dust distribution on Mars’s nightside, L s =75°-145°, MY 31. Dark areas indicate well-mixed. Lighter areas indicate strong layering in structure. Fig. 7 (top right): Cumulative distribution of night to day change in dust density-scaled opacity for the blue and red boxes in Fig. 6. Fig. 8 (bottom left): Example aerosol profiles from region of interest circled in Figure 6. The “doubly detached dust layer” suggests there is a second mode of DDL formation in northern spring and summer. Same great dayside injection… …different nightside distributions Longitude P R E S U R E (P A) But You Don’t Have To Take My Word for It… Guzewich, S.D., E.R. Talaat, A.D. Toigo, D.W. Waugh, and T. McConnochie (2013), High altitude dust layers on Mars: Observations with the Thermal Emission Spectrometer, J. Geophys. Res. Planets, 118, 1177-1194, doi: 10.1002/jgre.20076. Heavens, N. G., M. I. Richardson, A. Kleinböhl, D. M. Kass, D. J. McCleese, W. Abdou, J. L. Benson, J. T. Schofield, J. H. Shirley, and P. M. Wolkenberg (2011), The vertical distribution of dust in the Martian atmosphere during northern spring and summer: Observations by the Mars Climate Sounder and analysis of zonal average vertical dust profiles, J. Geophys. Res. Planets, 116, E04003, doi:10.1029/2010JE003691. A manuscript reporting this work is under review by J. Geophys. Res. Planets and is available from the presenter by request.

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